Power generation turbines are typically housed in containment areas to protect individuals in the event of an explosion. Sensors from the turbines communicate with instrumentation and equipment in the turbine control room via multi-conductor sensor cables. In the event of an explosion in the turbine containment area, when conventional multi-conductor cables with no gas blocking capabilities are used, high pressure, hazardous gases will travel through the interstitial spaces of the cables and will reach control rooms and may cause harm to people operating the control room. Historically, gas blocking is achieved only in a cable gland assembly connection to the frame wall. Such an approach, however, leaves a leak path through the interstitial space in the cable. A need exists for a multi-conductor cable that eliminates interstitial leak paths.
The marine industry has been using water blocked cables for many years. Such cables, however, would fail to prevent the leakage of hazardous high pressure gases in the event of an explosion. Furthermore, such cables cannot withstand the high cable operating temperature environment of a power generation turbine application (up to 200° C.).
The IEC (International Electro-technical Commission) released Specification EN-60079-14 in 2008. This specification covers instrumentation cables that are used on power generation turbines. A need therefore exists for cables that meet the new stringent IEC requirements. Although fluid blocking technology is used in water block cables, as noted previously, the temperature rating and pressure requirements of the “explosion proof” cables necessary to meet the IEC requirements are far beyond the capability of the technology in water block cables.
Recent changes to UL 1277 Impact Test requirements require that the two outer braids of a gas blocking cable be removed during impact testing. To meet the new requirements, the following steps have been taken to lessen impact to the plurality of insulated conductors within the cable. There is a need for a cable that meets gas block requirements while meeting UL 1277 requirements.